Current estimates place the prevalence of attention-deficit/hyperactivity disorder (ADHD) in the US at 3-5%. The usual age of first diagnosis is between 6-7 years of age when students are first entering school; however, many parents will argue that they observed signs/symptoms of ADHD much earlier. Intriguingly, of all 3-4 year old children diagnosed with ADHD (using traditional parent/teacher interview methods), only about 50% continue to meet diagnostic criteria at age 7. Previous attempts at achieving better diagnostic stability before the age of seven have expanded the number and kinds of behavior that are measured. Although these attempts have slightly improved predictability, no new gold standard for this age range has been achieved. The primary goal of this K01 research plan is to examine the development of the neural systems that mark the transition from signs and symptoms of ADHD to stable ADHD diagnosis. By using neuroimaging to better infer the underlying biology, better prediction of which children who exhibit elevated inattention and hyperactivity at age 3 will continue to exhibit these behaviors at age 7 and beyond may be achieved. Children who continue to meet diagnostic criteria for ADHD after the age of 7 are very likely to continue to meet diagnostic criteria across childhood, and in 40-70% of cases into adulthood. Even if they do not meet criteria for the disorder in adulthood they will, based on their childhood diagnosis, have increased risk for academic failure, social problems, substance use disorder, car accidents, and incarceration. Neuroimaging studies have associated deficits of cognitive control with differential activation of the prefrontal cortex in children and adolescents with and without ADHD ages 8 through adulthood. Less is known, however, about the neural basis of the development of cognitive control in younger children ages 3-7 and how this contributes to the development of ADHD. This is a major gap in knowledge, considering how crucial this time period may be to the continued expression of ADHD symptomology. Researchers have found it challenging to investigate the neuro-developmental roots of executive function because of limitations in our ability to image the brain in children this young. However, techniques allowing EEG data collection in 3-4 year olds and fMRI data collection in 5-7 year olds have recently been perfected and are proposed here.